Theory.
The Y-H system has a more extensive history than S-H or La-H systems, partly because some of the design of La-H materials included the isovalent Y-H system. Li et al. reported[1]} materials design for this system soon after their 2014 work on SH\(_2\)  noted in Sec. V.B. Their 2015 structure search at high pressure identified YH\(_3\) , a bct YH\(_4\)  lattice with both atomic H sites and H\(_2\)  units, and bcc YH\(_6\)  with a sodalite structure, [Fig. REF (b), Y surrounded by 24 H atoms] as promising candidates. The latter two had predicted T\(_c\)  around 90K and 260K, respectively, in the (encouragingly low) 120 GPa pressure range.
